Advanced Cardiac Care in the StreetsUnderstanding EKGs

Ray Taylor Valencia Community College

Advanced Cardiac Care in the StreetsUnderstanding EKGs

Ray Taylor Valencia Community College

ElectrophysiologyElectrophysiology

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Basic ElectrophysiologyBasic Electrophysiology

ObjectivesObjectives State the two basic myocardial cell groupsState the two basic myocardial cell groups Describe the function of each myocardial Describe the function of each myocardial

cell groupcell group Discuss the four primary properties of Discuss the four primary properties of

cardiac cellscardiac cells List the three major electrolytes that affect List the three major electrolytes that affect

cardiac functioncardiac function

Basic ElectrophysiologyBasic Electrophysiology

Objectives [ continued ]Objectives [ continued ] Describe the movement of ionsDescribe the movement of ions Describe cardiac depolarizationDescribe cardiac depolarization Describe cardiac repolarizationDescribe cardiac repolarization Define refractory periodDefine refractory period Describe the absolute refractory periodDescribe the absolute refractory period Describe the relative refractory periodDescribe the relative refractory period

Cardiac PhysiologyCardiac Physiology

ElectrophysiologyElectrophysiology Cardiac MuscleCardiac Muscle

AtrialAtrial VentricularVentricular Excitatory and Excitatory and

Conductive FibersConductive Fibers Intercalated discsIntercalated discs SyncytiumSyncytium

Atrioventricular Atrioventricular BundleBundle

DepolarizationDepolarization

Basic Cell GroupsBasic Cell Groups

Specialized Pacemaker CellsSpecialized Pacemaker Cells do not have the ability to contractdo not have the ability to contract responsible for controlling rate and rhythm responsible for controlling rate and rhythm

by coordinating regular depolarizationby coordinating regular depolarization found in electrical conduction system of the found in electrical conduction system of the

heartheart primary function is generation and primary function is generation and

conduction of electrical impulsesconduction of electrical impulses

Basic Cell GroupsBasic Cell Groups

The Myocardial Working CellsThe Myocardial Working Cells responsible for generating the physical responsible for generating the physical

contraction of heart cellscontraction of heart cells muscular layer of atrial walls and thicker muscular layer of atrial walls and thicker

muscular layer of ventricular wallsmuscular layer of ventricular walls primary functions are both contraction and primary functions are both contraction and

relaxationrelaxation physical contraction of myocardial tissue physical contraction of myocardial tissue

actually generates blood flowactually generates blood flow

Basic Cell GroupsBasic Cell Groups

ThresholdThreshold - - point at point at which a stimulus will which a stimulus will produce a cell responseproduce a cell response

““All or None” All or None” phenomenonphenomenon - stimulus - stimulus is strong enough for is strong enough for cardiac cells to reach cardiac cells to reach threshold, ALL cells will threshold, ALL cells will respond to this stimulus respond to this stimulus or none will respond.or none will respond. SyncytiumSyncytium

Cardiac PhysiologyCardiac Physiology

Cardiac Cell Cardiac Cell CharacteristicsCharacteristics

PropertiesProperties AutomaticityAutomaticity ExcitabilityExcitability ConductivityConductivity ContractilityContractility

Primary Cardiac Cell CharacteristicsPrimary Cardiac Cell Characteristics

1. 1. AutomaticityAutomaticity - [ electrical function ] - [ electrical function ] ability of cardiac pacemaker cells to ability of cardiac pacemaker cells to spontaneously generate own electrical spontaneously generate own electrical impulses without external stimulation impulses without external stimulation

2. Excitability2. Excitability - [ electrical function ] - [ electrical function ] ability of cardiac cells to respond to ability of cardiac cells to respond to electrical stimulus is also referred to as electrical stimulus is also referred to as irritabilityirritability

Primary Cardiac Cell CharacteristicsPrimary Cardiac Cell Characteristics

3.3. ConductivityConductivity - [ electrical function ] ability of - [ electrical function ] ability of cardiac cells to receive an electrical stimulus cardiac cells to receive an electrical stimulus and then to transmit the stimulus to other and then to transmit the stimulus to other cardiac cells, so they function collectively as cardiac cells, so they function collectively as a unita unit

4. 4. ContractilityContractility - [ mechanical function ] also - [ mechanical function ] also referred to as rhythmicity, is the ability of referred to as rhythmicity, is the ability of cardiac cells to shorten and cause cardiac cardiac cells to shorten and cause cardiac muscle contraction in response to an muscle contraction in response to an electrical stimulus electrical stimulus

Major Electrolytes That Affect Cardiac FunctionMajor Electrolytes That Affect Cardiac Function

Myocardial cells bathed in electrolyte Myocardial cells bathed in electrolyte solutionssolutions ElectrolyteElectrolyte - substance or compound - substance or compound

whose molecules dissociate into charged whose molecules dissociate into charged components, orcomponents, or ionsions. .

Produce + charged ions [ Produce + charged ions [ cationcation ] and ] and

- charged ions [ - charged ions [ anionanion ] when placed in ] when placed in waterwater

Three Major Cations That Affect Cardiac FunctionThree Major Cations That Affect Cardiac Function

PotassiumPotassium [ [KK+] - performs major +] - performs major function in cardiac depolarization and function in cardiac depolarization and repolarizationrepolarization

SodiumSodium [[NaNa] - performs vital part in ] - performs vital part in depolarization of myocardiumdepolarization of myocardium

CalciumCalcium [[CaCa] - important function in ] - important function in depolarization and myocardial depolarization and myocardial contractioncontraction

Movement of IonsMovement of Ions

Ionic difference on two sides of cellIonic difference on two sides of cell Potassium ionPotassium ion -concentration greater inside cell -concentration greater inside cell Sodium ionSodium ion -concentration greater outside cell -concentration greater outside cell Sodium-potassium exchange pumpSodium-potassium exchange pump - active - active

transport, potassium / sodium moved in and out of transport, potassium / sodium moved in and out of cell through cell membranecell through cell membrane

During During polarized or resting statepolarized or resting state, inside of cell , inside of cell electrically negative relative to outside of cellelectrically negative relative to outside of cell

Cardiac DepolarizationCardiac Depolarization

When impulse develops and spreads When impulse develops and spreads throughout the myocardium, changes occur in throughout the myocardium, changes occur in heart muscle fibersheart muscle fibers Cardiac DepolarizationCardiac Depolarization - sodium ions rush into - sodium ions rush into

cell (fast channel), changing interior charge to + cell (fast channel), changing interior charge to + after cell stimulatedafter cell stimulated

Calcium enters slow channel maintaining contractionCalcium enters slow channel maintaining contraction

Cardiac RepolarizationCardiac Repolarization - sodium ions return to - sodium ions return to outside of cell, potassium returns to inside of celloutside of cell, potassium returns to inside of cell

Cardiac Physiology/Ion ShiftsCardiac Physiology/Ion Shifts

Cardiac Cardiac DepolarizationDepolarizationResting PotentialResting PotentialAction PotentialAction PotentialRepolarizationRepolarization

Terms to RememberTerms to Remember

Resting Resting MembraneMembrane PotentialPotential - state of - state of cardiac cell- inside cardiac cell- inside negative-outside negative-outside positivepositive

Action PotentialAction Potential - - change in polarity; change in polarity; produces change in produces change in cell electrical charge cell electrical charge caused by caused by stimulation of stimulation of myocardial cellsmyocardial cells

Terms to RememberTerms to Remember

SyncytiumSyncytium - - cardiac muscle cell cardiac muscle cell groups that are groups that are connected together connected together and function as a and function as a unitunit

Polarized StatePolarized State - - resting state of resting state of cardiac cell, inside cardiac cell, inside of cell is electrically of cell is electrically negative relative to negative relative to outsideoutside

Refractory PeriodsRefractory Periods

Attempts to ensure muscle is totally Attempts to ensure muscle is totally relaxed before another action potential relaxed before another action potential or depolarization can be initiatedor depolarization can be initiated

Atrial muscleAtrial muscle = 0.15 sec. = 0.15 sec. Ventricular muscleVentricular muscle = 0.25 to 0.3 sec. = 0.25 to 0.3 sec. Period of rest is referred to asPeriod of rest is referred to as

Cardiac RepolarizationCardiac Repolarization

Two Stages of RepolarizationTwo Stages of Repolarization

Absolute Absolute RefractoryRefractory PeriodPeriod - cardiac cell unable - cardiac cell unable to respond to new to respond to new electrical stimulus, electrical stimulus, cannot cannot spontaneously spontaneously depolarizedepolarize

Two Stages of RepolarizationTwo Stages of Repolarization

Relative RefractoryRelative Refractory PeriodPeriod - - repolarization repolarization is almost complete, is almost complete, cardiac cell can be cardiac cell can be stimulated to contract stimulated to contract prematurely if stimulus prematurely if stimulus is stronger than normalis stronger than normal

Thank you!